The disclosure of Japanese Patent Application No. 2000-355952 filed on Nov. 22, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an engine of a vehicle such as a motor vehicle, and more particularly to a control relating to heating a fuel supplied to an engine.
2. Description of Related Art
In an engine of a vehicle, such as a motor vehicle, it has been a common practice to provide an electric heater at a fuel injection valve, that injects a fuel into an engine combustion chamber, for heating the fuel injection valve to inject thus heated fuel. Further, there have been suggested various kinds of inventions which improve durability of the heater by preventing overheat thereof and which control heating of the fuel by the heater based on a temperature of atmospheric air and the engine or a combustion state of the fuel or the like. Examples of the inventions mentioned above are disclosed in Japanese Patent Application Laid-open Nos. 5-288131, 11-148441, and the like.
These conventionally given suggestions correspond to inventions relating to how heating of the fuel should be controlled according to the temperature of the atmospheric air and the engine or the combustion state of the fuel or the like, exclusively to improve a fuel heating performance of the heater and a durability of the heater or improve a startability of the engine through heating of the fuel by the heater.
In the engine provided with the heater for heating the fuel, conventionally in general, application of electric current to both of a motor for starting the engine and the heater for heating the fuel is simultaneously started at a time of starting the engine. This is because heating of the fuel by the heater improves a startability when the engine is cold, and this operation is as a matter of course when consideration is given to improvement of an exhaust property at a time of starting the engine under a cold temperature. It is true that in view of the object and effect of the heater operation, it can be considered that the heater is started at the same time the engine is started.
However, the above-mentioned heater for heating the fuel consumes a lot of electric power for operation, and the consumed electric power corresponds to a significantly heavy load for an electric power storage device having a limited capacity. Accordingly, in the case of operating the heater for heating the fuel at the same time driving of the engine is started by the motor for starting the engine, two heavy loads are simultaneously applied to the electric power storage device having a limited capacity. This reduces an electric power supply to each of the loads (the motor for starting the engine and the heater for heating the fuel). Accordingly, on one hand, a driving revolution for starting the engine is decreased, thereby delaying the engine to start running on its own, and on the other hand, a degree of heating the fuel by the heater is reduced, thereby delaying the engine to start running on its own and prolonging a discharge of unburned content at start-up, so that a synergistically adverse effect is generated with respect to an improvement of the engine startability and controlling of unburned content emitted at start-up. This becomes conspicuous at a time when a storage state of the electric power storage device is lowered, and a specific attention will be necessary.
The invention has been made by focusing attention on the fact that there is a risk that an adverse result may be brought about with respect to an object and an operation and effect of a heater for heating a fuel in an engine depending on operating periods of the heater. An object of the invention is to improve an operating period control of the heater for heating the fuel.
In accordance with one exemplary aspect of the invention, there is provided a method for controlling an operation of a heater for heating a fuel in an engine started by being driven by a starting motor, in which the operation of the heater is started after the operation of the starting motor is substantially terminated at a time of starting the engine.
In the exemplary aspect mentioned above, the operation of the starting motor may be substantially terminated at a time when a switch of a power circuit in the starting motor is opened.
Further, in the above exemplary aspect, the operation of the starting motor may be substantially terminated at a time when the engine is first able to run on its own.
It is true that a startability of the engine under cold temperature is improved by heating the fuel by the heater. However, considering an improvement of the engine startability by the fuel heating in more detail, it can be seen that the fuel heating actually becomes effective at a time when the engine is able to run on its own and the operation thereof is to be stabilized through warm-up. The respective elapses of an engine starting motor operating command signal, an electric power consumption of the motor and an engine revolution at a time of starting the engine are generally as shown in FIG. 1. In a normal engine start, the engine is able to run on its own at a time t1 which is less than 1 second after driving of the engine is started by the motor, and thereafter, the engine revolution is increased by the power of the engine itself. On the contrary, with respect to the heating of the fuel by the heater, even when the heater is provided at a fuel injection valve closest to an injection end of the fuel, a time delay exceeding 1 second is generated until the heat generated by an electric current application is substantially transmitted to the fuel, because the heater itself and the fuel injection valve have a considerable heat capacity. Accordingly, even if the electric current application to the heater is started at the same time the electric current application to the motor is started, the fuel injected before the engine is able to run on its own would be barely heated.
Accordingly, it is assumed that the engine is able to run on its own when driven at a predetermined revolution or more until a predetermined times even when the engine is cold without the fuel being particularly heated at that time. Further, if the fuel is heated after the engine becomes capable of running on its own, an improved fuel explosion can be obtained and the engine can start up more rapidly and more smoothly. Further, if the fuel is heated during the time, it is possible to prevent the fuel from attaching to a wall surface of a combustion chamber, a start-up operation of the engine can be performed at stoichiometric air fuel ratio, and an exhaust property at a time of starting the engine can be improved. Accordingly, when the engine is driven by the motor, it is preferable to restrict the electric current application to the heater, increase an amount of electric current application to the motor as much as possible, increase an engine driving revolution by the motor, and ensure that the engine is able to run on its own at an early stage.
If a time, when the operation of the starting motor is substantially terminated, for starting the electric current application to the heater is set to a time when the switch of the power circuit for applying an electric current to the starting motor is opened, as a time t3 shown in FIG. 1, it is possible to securely prevent the motor load and the heater load from being simultaneously applied to the electric power storage device. However, in this case, when the electric current application to the motor is executed for a time longer than necessary, there is a problem that the operation start of the heater is delayed more than necessary.
On that point, if a time when the operation of the starting motor is substantially terminated is set to a time when the engine becomes capable of running on its own, it is possible to avoid the problem that the operation start of the heater is delayed more than necessary due to the electric current application to the motor being executed for a time longer than necessary as mentioned above. In this case, the engine is judged to be capable of running on its own at a time when self-running of the engine has progressed at a certain degree to be sure, whereby the engine driving load applied to the motor is largely reduced and the operation of the motor is not completely terminated but substantially terminated, as at a time t2 shown in FIG. 1. Accordingly, when the electric current application to the heater is started, the switch of the motor power circuit is still closed, and even if a state occurs where the load of the motor and the load of the heater are simultaneously applied to the electric power storage device, the load applied by the motor has been already largely reduced. Therefore the heater can immediately obtain a strong electric current from the electric power storage device to operate.
In the exemplary aspect mentioned above, the operation of the heater can be such that a plurality of heaters with respect to all the cylinders are simultaneously started operating upon substantial termination of the operation of the starting motor. Further, when a plurality of heaters are separated into groups, the operation of the heaters may be started step by step by each group upon substantial termination of the starting motor.
In this case, if the heaters with respect to all the cylinders are separated into a plurality of groups and the operation of the heaters can be started step by step by each group, even in the case that the operation of the heater is started at a time when the operation of the motor is not yet completely terminated as mentioned above, it is possible to better avoid the load increase caused by the overlapped loads by starting the operation of the heaters step by step by each group.